1. Field of the Invention
The present invention relates to an inter-node connection method and apparatus, and in particular to a method and apparatus for mutually connecting nodes (terminals) through address spaces managed with different allocation policies, that is a private IP address network and a global IP network.
2. Description of the Related Art    (1) Kinds of IP Address and Translation (Conversion) Method Thereof
An IP address is defined as comprising two kinds, i.e. a global IP address and a private IP address based on an allocation (assignment) policy as noted below (see e.g. non-patent document 1):                Global IP address: IP address uniquely allocated for a device connected to the Internet;        Private IP address: IP address uniquely allocated for a device connected to a network within an organization such an intranet. While it is possible to freely make an address allocation within an organization even without applications, address uniqueness is not guaranteed over the Internet, so that communications cannot be made over the Internet as it is.            (2) Address Translation
In order for a node having a private IP address to communicate with a node having a global IP address, an address translation is required between both of the addresses. A device having a NAPT (Network Address Port Translation: IP masquerade) (hereinafter, referred to as “NAPT device”) as a representative technique comes into widespread use (see e.g. non-patent document 2).                NAPT device: In a case as shown FIG. 16 where a plurality of nodes each having a private IP address, namely, a local (private) node (hereinafter, simply referred to as a node) N1 of a private IP address “192.168.0.10”, and a local node N2 of a private IP address “192.168.0.20” reside in a private IP address network NW1, and also a global node N3 of a global IP address “202.232.2.13” resides within a global IP address network NW2, the node N3 cannot determine only with a single global IP address from which node of a private IP address it has received a packet (frame). Therefore, the provision of a NAPT device AC including therein a bind table BT can associate the IP addresses with the port numbers and so relate the packet to a local node.        
For example, the NAPT device AC having first received a packet from the node N1 having the private IP address “192.168.0.10” prepares an entry of the bind table BT by allocating thereto a port (IP address “202.19.176.120”: port number “10080”) at the end (on the side) of its own global IP address network NW2. Namely, this bind table BT has an entry prepared with a frame transmitted by the node N1 in which a port at the end of the global IP address network NW2 of the NAPT device AC is allocated, so that the NAPT device AC enables only an address translation from the local nodes N1 and N2 toward the global node N3.
Accordingly, in a case as shown in FIG. 17 where the nodes N1 and N2 are set up in the private IP address spaces NW1 and NW3 which are mutually different and are mutually connected with NAPT devices NC1 and NC2 as well as a global IP address network NW2 connecting both devices, no frame can reach into the private IP address networks from the global IP address network, disabling communications between the nodes N1 and N2 (at step T0).
(3) STUN
As a measure for solving such as a problem of a NAPT device as indicated above (2), a STUN (RFC 3489) system is mentioned (see e.g. non-patent document 3).
This STUN system solves such a problem by providing, as shown in FIG. 18, an association server (hereinafter, occasionally simply referred to as a server) SRV which manages the following entries (information) in the form of a table TBL at the end of the global IP address network NW2, where both transmitting/receiving nodes behave as if they are positioned at the transmitting end since both transmit a frame in advance of the reception. It is to be noted that STUN is applied to UDP, not to TCP.
[Entries of Table TBL Managed by Association Server SRV]
                Global IP address (WAN IP address) and global port (WAN port) number of the NAPT devices AC1 and AC2;        Identification number of node (IDs uniquely allocated to all nodes);        Local port (LAN port) number of node.        
Namely, from the nodes N1 and N2, a LAN port allowing the association server SRV to connect to the outside is preliminarily registered, while the association server SRV allocates unique IDs (hereinafter, occasionally referred to as node ID) to the nodes N1 and N2, whereby the association server SRV prepares entries of the management table TBL.
In the following, a procedure of an inter-node connection (communication) will be described referring to FIG. 18, where it is to be noted that this figure shows an example of a connection from a port 700 of the node N1 to a port 300 of the node N2 and that occasionally ports and port numbers are mutually denoted with identical reference numerals:
Step S11:
The source node N1 transmits to the association server SRV a “connection request” frame composed of a node ID “0002” and a local port number “300” of the communication destination node N2 with which the source node Ni desires to communicate.
Step S12:
The association server SRV notifies to the communication source node N1 and the communication destination node N2 respectively an IP address and a port number at the end of the global IP address network NW2 of opposed NAPT devices AC2 and AC1. Namely, the association server SRV notifies a global IP address and a port number “100.101.102.10:8700” of the NAPT device AC1 to the node N2, and notifies a global IP address and a port number “200.50.40.24:4100” of the NAPT device AC2 to the node N1.
Step S13:
The node N1 transmits a frame to the global IP address and the port number (200.50.40.24:4100) of the NAPT device AC2 which forms a Peer notified at the above step S12, whereby the NAPT device AC1 binds (associates) the private IP address and the port number of the node N1 with the global IP address and the port number of the NAPT device AC2, respectively.
Step S14:
The node N2 transmits a frame to the global IP address and the port number (100.101.102.10:8700) of the NAPT device AC1 which forms a Peer notified at the above step S12, whereby the NAPT device AC2 binds (associates) the private IP address and the port number of the node N2 with the global IP address and the port number of the NAPT device AC1, respectively.
Step S15:
The nodes N1 and N2 establish a direct session (path) through the NAPT devices AC1-AC2, not through the association server SRV.
Step S16:
Namely, notifications of the global IP address and the port number of the NAPT devices to the communication source node and the communication destination node respectively as indicated at the above step S12 enable accesses to be commenced from the nodes N1 and N2 at the ends of the private IP address networks NW1 and NW3 respectively at the above steps S13 and S14.
Step S17:
On the other hand, as prior art which improves a transfer efficiency by a mutually direct communication between servers, there have been proposed equipment, mechanism, method, and medium recording them, for dynamically exchanging bidirectional data among devices having private address and devices having global address going over network routers, in which the P-side device and the G-side device are connected to a session management server (S) installed in the G-side, and the S supervises data area which is allocated uniquely; data are transferred directly between devices not passing through the S, according to the obtained session information, such as data transfer request, regarding own device; direct data transfer from the G-side to the P-side becomes possible by replacing it to direct data acquisition from the P-side to the G-side; this being applied to the communication between P-side devices separated by the G-side network (see e.g. patent document 1).
[Non-patent Document 1]
    http://www.ietf.org/rfc/rfc1918.txt?number=1918[Non-patent Document 2]    http://www.ietf.org/rfc/rfc3022.txt?number=3022[Non-patent Document 3]    http://www.ietf.org/rfc/rfc3489.txt?number=3489[Patent Document 1] Japanese patent application laid-open No. 2003-101590
An association server of the above mentioned STUN system makes an access to a node with a management table having entries (registrations) of a port number which each node opens to the public. In the example of FIG. 18, the table TBL of the association server SRV has five ports' entries.
Therefore, the increase of port number for entry will increase the cost of the resource (memory, hard disk, CPU etc.) of the association server, resulting in a limited scalability.